The third of three times in the show that the character of Lt. Arex does not appear. He also does not appear in Yesteryear (1973) and The Slaver Weapon (1973).
This is one of three episodes in which Uhura does not appear, the others being Yesteryear (1973) and The Jihad (1974).
The title is from a quote in the 1878 novel 'Molly Bawn' by Margaret Wolfe Hungerford: "Beauty is in the eye of the beholder."
Hard-core Star Trek (1966) fans are quick to point out that Markel and Bryce - not Enterprise crew - shouldn't be wearing the "arrowhead" Enterprise insignia; however, since the Star Trek movies and later TV series show all of Starfleet using the symbol, some fans postulate that perhaps its use indicates it had already been adapted as the universal Starfleet emblem.
This takes place in 2269.